doctor's office; clinic; surgery
Refers to a medical facility where a doctor sees patients, typically smaller than a hospital. Often used for private practices or small clinics.
I caught a cold, so I went to a nearby clinic.
This doctor's office operates by appointment.
My father opened a clinic in this town.
The son took over his father's clinic.
診療所 is a slightly more formal/administrative term for a small medical facility, often used in official contexts, while 医院 is the everyday word for a doctor's practice.
Compound of 医 (medicine, doctor) and 院 (institution, building). The spelling 醫院 is the kyūjitai form.